Subject: Re: [Sip] I-D on handling large UDP responses

From: Cullen Jennings <[email-masked]>
Date: Mon, 4 Dec 2006 06:39:32 -0800

Hmm - clearly whatever Scott and I had agreed might work is probably  
irrelevant at this point since it clearly was not something we all  
agreed to or can even remember. It was just an hallway conversation  
between Scott and I. BTW, my vague recollection of it was I thought  
we had agreed that saying the response body would not be included  
unless it was less the total message was less than 1500 octets and  
provide advice on how to trim it down to be that size.

On Nov 20, 2006, at 9:05 AM, Scott Lawrence wrote:

> On Mon, 2006-11-13 at 11:20 +0100, Drage, Keith (Keith) wrote:
>> Question repeat, as it does not seem to have been answered.
>
>>> From: Drage, Keith (Keith) [mailto:[email-masked]]
>>> Sent: 04 October 2006 19:46
>>> To: Cullen Jennings; Dean Willis
>>> Cc: IETF SIP List; Vijay K. Gurbani
>>> Subject: RE: [Sip] I-D on handling large UDP responses
>>>
>>> Can you tell us what you agreed on. The proceedings seem to
>>> have missed it, and I don't remember it appearing on the list.
>
> I am not at all sure that we agreed on anything with respect to this.
>
> -- 
> Scott Lawrence  tel:+1-781-938-5306;ext=162 or  
> sip:[email-masked]
>   sipXpbx project coordinator - SIPfoundry    http:// 
> www.sipfoundry.org/sipX
>   Chief Technology Officer    - Pingtel Corp. http://www.pingtel.com/

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---

From: Scott Lawrence <[email-masked]>
Date: Mon, 04 Dec 2006 10:03:49 -0500

> provide advice on how to trim it down to be that size.

That matches my recollection regarding the handling of hop limit
responses (and any other similar diagnostic responses), but I didn't
think that was the current question.  

I was referring to a general rule for what to do with _any_ large
response on a path that includes UDP.  My recollection is that there are
essentially three points of view on this:

      * Do Nothing - let UDP either work or not (there seemed to be
        important disagreement on how often this is a problem), and if
        it doesn't work, don't do anything different to make it easier
        to detect why not.

      * Diagnostic Provisional Response - add a small 1xx response or
        responses (as described in
        draft-gurbani-sip-large-udp-response-00) to aid in diagnosis of
        failures.  This ran into objections from some people with
        respect to non-INVITE transactions, and from others who seemed
        to object on broader grounds.

      * Always Return Error - instead of returning whatever final
        response you were going to return (whether positive or
        negative), return an error indicating that the response would be
        too large.

Alas, I think we've only gotten as far as the 'Rough' in 'Rough
Consensus' on this.

Obviously, I prefer some form of Diagnostic Provisional response.  I do
believe this is a significant problem.  I prefer the diagnositc approach
because it allows things to work if the large UDP response actually gets
through, but gives you some hint as to why not when it doesn't.   I
think that the relative cost of the extra 1xx is acceptable when
compared to the cost of the retransmissions when things are broken.

-- 
Scott Lawrence  tel:+1-781-938-5306;ext=162 or sip:[email-masked]
  sipXpbx project coordinator - SIPfoundry    http://www.sipfoundry.org/sipX
  Chief Technology Officer    - Pingtel Corp. http://www.pingtel.com/